'I found it on Google, so that makes it alright!' No, no, and no. Just because you found an image on the Intergoogles does not make it free to use. How many times have we been through this? I've lost count, I'm sure. It's simple: unless the copyright owner says otherwise, you can't use her or his photos without permission. There are some images that are free to use, but you have to search for them specifically. Thankfully, Google has just made that easier.
To be fair, Google Image Search has allowed for refined searches for quite some time, but now they've made it more obvious and easier. Hit the 'Search tools' button and it presents a series of drop-down menus that allow you to select the size, colour, age, file type, and licensing options for your desired image.

Searchers can choose licences covering available for reuse, commerical reuse, reuse with modification, and commercial reuse with modification. So whether you need a poinsettia to illustrate a blog post or a giraffe to add to a surreal composite, the search tools to find them are at your fingertips.

According to the tweet from Googler Matt Cutts, the suggestion for the refinement came from law professor Lawrence Lessig, who's heavily involved in the Creative Commons movement.

It will still be incumbent upon anyone wanting to reuse an image to double-check its rights and ensure that they comply with any caveats, for example proper attribution, that might be ascribed to it. However, together with Bing's refined image licence search, there are fewer and fewer excuses of the whine of 'But I found it on the Internet!' when it comes to image theft an misuse.